Transmitting video signals over unshielded twisted pair (“UTP”) cable is advantageous for a variety of reasons. UTP has become ubiquitous in modern business and residential settings. For example, CAT5 cable (a type of UTP cable) includes several twisted pair conductors, and may be used, for example, to transmit keyboard, video monitor, and mouse (“KVM”) signals within a computer system. Cost savings for UTP cabling over, for example, coaxial cabling, can be significant.
Two issues that may arise when transmitting video over UTP are nonlinear signal attenuation and signal time skew.
Signal attenuation is caused by the frequency domain characteristics of the cable, and may be thought of as a type of signal distortion in the frequency domain. For example, if the cable is low-pass in nature, attenuation of the higher frequencies within a signal may cause a loss of information, such as a loss of definition of the rising edges of impulses.
The time skew as between two signals being transmitted on different twister pairs within a UTP cable may be caused by the different physical lengths of cable pairs within the UTP cable. The time skew may cause like features of the two signals to reach the end of the UTP cable at different times. This may be thought of as a type of signal distortion in the time domain.
FIG. 1 shows a signal chain 100 with equalization 103 to compensate for the signal attenuation, and a delay line 104 to compensate for the signal time skew. FIG. 2 shows a typical line of video (e.g. a white line), and how the signal may look at different points in the signal chain (a-d). The circuit 100 of FIG. 1 requires a user to manually calibrate/adjust the “Equalizer Adjust” and “Delay Line Adjust” inputs to get acceptable picture quality.